Water mass export from Drake passage to the Atlantic, Indian and Pacific Oceans: a Lagrangian model analysis.

The northward export of intermediate water from Drake Passage is investigated in two global ocean general circulation models (GCMs) by means of quantitative particle tracing diagnostics. Our study shows that a total of about 23 Sv is exported from Drake Passage to the Equator. The Atlantic and Pacific Oceans are the main catchment basins with 7 and 15 Sv, respectively. Only 1-2 Sv of the water exported to the Atlantic Equator follow the direct cold route from Drake Passage, without entering the Indian Ocean. The remainder loops first into the Indian Ocean subtropical gyre and flows eventually into the Atlantic Ocean by Agulhas leakage.

We assess the robustness of a theory that relates the export from Drake Passage to the Equator to the wind stress over the Southern Ocean. Our GCM results are in reasonable agreement with the theory that predicts the total export.
However, the theory cannot be applied to individual basins because of interocean exchanges through the ``supergyre' mechanism and other nonlinear processes such as the Agulhas rings. The export of water from Drake Passage starts mainly as an Ekman flow just northward of the latitude band of the Antarctic Circumpolar Current south of America.
Waters quickly subduct and are transferred to the ocean interior as they travel equatorward. They flow along the eastern boundaries in the Sverdrup interior and cross the southern basins northwestward to reach the Equator within the western boundary current systems.